1. Field of the Invention
The present invention relates to a charging apparatus which charges a member to be charged using a corona charger. The charging apparatus is used for an electrophotographic image forming apparatus such as a copy machine, a printer, a facsimile, and a multifunction peripheral which includes a plurality of functions of copying, printing, and sending a facsimile.
2. Description of the Related Art
In a charging process, which is one of electrophotographic processes, a conventional electrophotographic image forming apparatus evenly charges a photosensitive member to be charged using a corona charger.
A configuration for charging with the corona charger can cause foreign substances (adhering substances) such as dusts and scattered toner suspended within the apparatus to adhere to a grid electrode.
If the foreign substances are adhering to the grid electrode, a charging efficiency decreases at a portion to which the foreign substances is adhering and uneven charge potential appears on the photosensitive member. Thus an output image may show non-uniform density.
Apparatuses discussed in Japanese Patent Applications Laid-Open Nos. 06-43735, 06-208283, and 2005-338797 are provided with a cleaning apparatus for cleaning a grid electrode by using a cleaning pad or a cleaning brush and cleaning the foreign substances adhering to an inner surface of the grid electrode of the corona charger.
However, the apparatuses discussed in Japanese Patent Applications Laid-Open Nos. 06-43735, 06-208283, and 2005-338797 cannot appropriately remove the foreign substances adhering to the inner surface of the grid electrode.
This is because if insulating foreign substances such as toner adheres to the grid electrode and receive corona discharge, an amount of charge thereof is increased, so that electrostatic force of the foreign substances adhering to the grid electrode is increased.
The longer the foreign substances receives the corona discharge, the larger the electrostatic adhesion (referred to as “a reflection force”) of the foreign substances becomes. The electrostatic adhesion can be expressed by the electrostatic force together with a mirror image charge generated on the grid electrode, and is proportional to the square of the amount of the charge of the foreign substances.
In order to remove from the grid electrode the foreign substances rigidly adhering thereto, a method is considered for increasing a cleaning ability of the cleaning apparatus, for example, by strongly pressing the cleaning brush against the grid electrode.
However, such method may cause an adverse effect since the foreign substances may be rubbed against the grid electrode. As a result, the foreign substances are fusion-bonded to the grid electrode and cause the uneven charge potential on the photosensitive member and non-uniform density in an output image.